1. Field of Invention
The present invention relates to a gate driving circuit. More particularly, the present invention relates to a gate driving circuit in a liquid crystal display.
2. Description of Related Art
In a general liquid crystal display, the driving circuit is one of the most significant components and an essential factor of product quality and cost. FIG. 1 shows a gate driving circuit of a general liquid crystal display. The gate driving circuit 100 includes driving circuit units 102 and a control unit 104. The control unit 104 generates a power source VSS, and outputs clock signals CK and XCK whose phases are opposite to each other, so as to control each of the driving circuit units 102. The driving circuit units 102 sequentially output driving signals G1, G2, . . . , GN to the corresponding scan lines.
First of all, the control unit 104 transmits a start signal ST to the 1st driving circuit unit 102, so as to drive the 1st driving circuit unit 102 to output the driving signal G1. Then, the 1st driving circuit unit 102 transmits the driving signal G1 to the 2nd driving circuit unit 102, so as to drive the 2nd driving circuit unit 102 to output the driving signal G2. The rest of the driving circuit units 102 output the driving signals as described above.
Additionally, the driving signal G2 output from the 2nd driving circuit unit 102 is transmitted back to the 1st driving circuit unit 102, so as to release the accumulated charges of the 1st driving circuit unit 102. That is, the driving signal output from the next driving circuit unit 102 is transmitted back to the previous driving circuit unit 102, so as to release the accumulated charges of the previous driving circuit unit 102.
FIG. 2 shows the driving circuit unit shown in FIG. 1. The transistor M3 receives the driving signal output from the next driving circuit unit 102. When the transistor M3 receives the driving signal output from the next driving circuit unit 102 to be turned on, the charges accumulated in the node Q are released through the transistor M3. Therefore, the driving circuit units 102 can output more accurate driving signals and be used as long as possible. However, the last driving circuit unit 102 does not receive any signal to release the accumulated charges thereof, so the last driving circuit unit 102 usually has more and more accumulated charges as operational time goes on, so that the last driving circuit unit 102 cannot operate as effectively as the others.
For the foregoing reasons, there is a need to solve the problem of accumulated charges in the last driving circuit unit.